In the field of operator control elements, displays formed e.g. by a series of LEDs are known, which indicate a set value. This may be a row of LEDs, i.e. light-emitting diodes, which are arranged side by side and of which one element emits light and indicates an actual value. As a rule, the luminescent elements arranged in a row are suitably labelled to enable an association with a quantity such as e.g. a display in “dB” for volume control. Changeover to another value is effected mechanically e.g. by means of momentary-contact switches. Generally, to increase and reduce the value one mechanical momentary-contact switch is used in each case. A change of value effected by pressing the appropriate momentary-contact switch is indicated by the appropriate LED in the row by virtue of a positional variation in the display.
FIG. 1 shows such an LED display known from the prior art, wherein the position of the LED and hence also e.g. the “volume level” may be adjusted by means of the plus and minus keys. The advantage of such an arrangement lies in the clear overview of the set position and in the spontaneous operator controllability. The drawback is, however, the need for mechanical cutouts in the operator control panel and the provision of appropriate keys.
From DE 43 36 669 C1 a touch panel is known, comprising optical sensors, which are associated with different actuating surfaces and react to the shading of a sensor surface corresponding to the size of a finger. The acquisition of the ambient light is therefore the information to be processed. Usually, for this purpose, a means other than the means used to generate a light signal is used. For indicating a value that is to be displayed an additional lighting display unit is required. The opto-receivers and opto-transmitters may be operated exclusively in a pulsed manner, which is disadvantageous for the discrete alteration of a value that is to be set (cf. also DE 40 07 971 A1 in the infrared range).
The acquisition of information, which is needed to vary a value to be set at an operator panel, may also be effected by means of touch-sensitive switching devices according to DE 694 19 735 T2 or DE 36 85 749 T2, which through the acquisition of a capacitance correspond with the optical display unit to be operated; because of its sensitivity to moisture, however, this use is restricted to specific areas.
DE 39 32 508 A1 shows a conventional reflection light barrier without a discrete control facility. Transmitters and receiving elements always have to be provided separately. DE 28 24 399 A1 discloses an optical switch with separate transmitters and receivers. In both cases, the light barriers formed thereby are only the means of setting the display and not the display means itself.
From U.S. Pat. No. 5,327,160 a touch fader as a remote control is known, which may be operated only in the switching mode.
Arrangements of light-emitting diodes, which may be used in turn both as a light-emitting and as a light-receiving element and the optical signal of which directly reproduces the value to be displayed, which may moreover be controlled so as to follow the movement of a finger or of a comparable body in order thereby to reach the value to be set, but which may also be operated in clocked manner and thus spontaneously, are not known from the prior art.